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871.
872.
Urkowitz H. Geisler J.D. Ricciardi N.A. 《IEEE transactions on aerospace and electronic systems》1973,(4):486-494
The Doppler sidelobes of a received pulse burst may be partially controlled by varying the amplitudes of the pulses in the burst or sequence upon transmission and/or reception. When there is a peak power limitation, weighting the amplitudes produces a loss in signal-to-noise ratio. A general expression is derived for the loss factor under the peak power limitation, and loss factor formulas are given for the following cases: Case A: Full nominal weights upon reception. Uniform weights on transmission. Case B: Square roots of the nominal weights on both transmission and reception. Case C: Full nominal weights on both transmission and reception. These cases are listed in order of increasing loss. Numerical results are tabulated for regular spacings and for the following nominal weights: 1) Dolph-Tchebycheff, 2) Taylor, 3) Hamming, and 4) Hann. 相似文献
873.
874.
The cell averaging LOG/CFAR receiver is a special implementation of a constant-false-alarm-rate (CFAR) receiver in which the noise level estimate is derived from a set of contiguous time samples of the output of a logarithmic (LOG) detector as obtained from a tapped delay line. This CFAR receiver is capable of operating over a larger dynamic range of noise levels than a conventional cell averaging CFAR receiver, but with somewhat poorer detectability. The performance in stationary Gaussian noise of the cell averaging LOG/CFAR receiver with no post-detection integration is determined in this paper. For a small number of reference noise samples, results were obtained by a Monte Carlo simulation using the technique of importance sampling. For a large number of reference noise samples, a second moment analysis gave the desired results. Both these results can be summarized in the following simple formula, NLOG = 1.65NLIN - 0.65, which relates the number of reference samples required by each of the two receivers for equivalent performance. Thus, for the cell averaging LOG/CFAR receiver to give the same detection performance as the conventional cell averaging CFAR receiver, the number of reference noise samples has to be increased by up to 65 percent. 相似文献
875.
Modeling and Estimation for Tracking Maneuvering Targets 总被引:3,自引:0,他引:3
Moose R.L. Vanlandingham H.F. Mccabe D.H. 《IEEE transactions on aerospace and electronic systems》1979,(3):448-456
A new approach to the three-dimensional airborne maneuvering target tracking problem is presented. The method, which combines the correlated acceleration target model of Singer [3] with the adaptive semi-Markov maneuver model of Gholson and Moose [8], leads to a practical real-time tracking algorithm that can be easily implemented on a modern fire-control computer. Preliminary testing with actual radar measurements indicates both improved tracking accuracy and increased filter stability in response to rapid target accelerations in elevation, bearing, and range. 相似文献
876.
Selected results from experiments investigating the potentially specific radiobiological importance of the cosmic HZE (= high Z, energetic) particles are discussed. Results from the Biostack space flight experiments, which were designed to meet the experimental requirements imposed by the microdosimetric nature of this radiation field, clearly indicate the existence of radiation mechanisms which become effective only at higher values of LET (linear energy transfer). Accelerator irradiation studies are reviewed which conform with this conjecture. The recently discovered production of "micro-lesions" in mammalian tissues by single HZE particles is possibly the most direct evidence. Open questions concerning the establishment of radiation standards for manned spaceflight, such as late effects, interaction with flight dynamic parameters, and weightlessness, are indicated. 相似文献
877.
878.
A closed-form solid-state solution for a simple one-dimensional smoother is presented. The target position-velocity dynamics are modeled as a linear discrete Gauss-Markov process: the discrete position measurements are assumed to be independent and identically normally distributed. Analytical results derived from estimating optimum steady-state position and velocity are given as well as the improvement provided by smoothing relative to pure filtering estimates. Analytical results, including appropriate limiting cases, show that the ratios of the RMS smoothing to the RMS filtering error are from 1/2 to 1 in position and from 1/2 to 1/√2 in velocity. As a numerical example a highly maneuvering target characterized by an acceleration width of 30 m/s2 is considered 相似文献
879.
880.
M.C. Zolcinski D.J. Forrest J.M. Ryan E.L. Chupp G. Kanbach C. Reppin E. Rieger G.H. Share 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(11):193-196
We have searched for anisotropic X-ray bremsstrahlung photon production from relativistic electrons by studying the heliocentric angular dependence of 53 flares detected at energies above 300 keV. We have found no evidence for a higher rate of detectable flares near the limb at the 80% confidence level. This result implies that the X-ray directivity as defined by the ratio of photon intensity at 75° and 0° of heliocentric angle is less than 1.5 above 300 keV and strongly rejects any flare model predicting X-ray production from a radial “beam” of energetic electrons. 相似文献